Cell planning within mobile communication systems, such as GSM is an important task for telephone operators to optimize the performance for mobile telephone users. The mobile communication system comprises a network containing a plurality of sites, each site have one or more antennas providing coverage for a cell coverage area. In a present cell planning tool, an operator provides measured data from selected points in the coverage area as input data to the cell planning tool. The input data is obtained by measuring the signal strength at the selected points. If a change occurs in the network during a network tuning stage, the measured signal strength cannot always be reused. This problem is solved by converting the measured signal strength at the selected points into path loss and use the path loss as input data in the cell planning tool. The path loss may be reused for all changes in the network, except for changes in the physical antenna position or frequency band changes.
The path loss is calculated by taking the transmitting power Ptx from the antenna and subtracting the known received signal strength indicator RSSI of a signal. The path loss equation may be expressed as:Path loss[dB]=Ptx[dBm]−RSSI[dBm],  (1)
The transmitting effective isotropically radiated power (EIRP) Ptx may be expressed as:Ptx[dBm]=Pin[dBm]+Gant[dB],  (2)where Pin is the known input power to the antenna and Gant is the effective antenna gain. The effective antenna gain Gant is calculated by estimating the angles of direction α (which could be expressed in Cartesian coordinates x,y,z or azimuth αazimuth and elevation αelevation) between the transmitting and receiving antennas and mapping these angles to the 3-dimensional antenna pattern.
In US 2002/0063656 A1, by Tanley J. Gutowski, a standard procedure for estimating the angles of directions is disclosed. A straight line is drawn from the transmitting antenna position to the receiving antenna position when calculating the path loss. This approach usually has enough accuracy but will produce erroneous results in specific environments with indirect signal paths, such as reflected signal paths in an area with high buildings.